As a light source for an ultraviolet irradiation apparatus used in a backlight illumination, photo-curing of an ultraviolet curing resin, sterilization, cleaning, a production process of a semiconductor, etc., a discharge lamp of high-pressure mercury, metal halide, or xenon has been mainly used in the related art. Light emitted from the light source composed of the discharge lamp include not only an ultraviolet region but also a wide range of wavelength regions from deep ultraviolet to far infrared. Therefore, in order to inhibit a temperature increase in an irradiated area or utilize needed ultraviolet rays effectively, a cold filter is necessary.
In contrast, an ultraviolet light-emitting diode (hereinafter referred to as “ultraviolet LED”) is characterized in that the ultraviolet rays having specified wavelengths can be emitted selectively. Therefore, the cold filer may not be used. However, an emission intensity (UV intensity) of the ultraviolet LED is small. When the ultraviolet LED is used as the light source for resin curing, backlight or other applications, a number of the ultraviolet LEDs should be used. The ultraviolet light-emitting apparatus using a number of ultraviolet LEDs to enhance the intensity and including a light source being as compact as possible is known: Specifically, there is a ultraviolet light-emitting apparatus including a plurality of light-emitting diodes for emitting ultraviolet rays being arranged to form one planar surface and to space equally each other on a concentric circle from a main light axis of the apparatus, collimating optical systems arranged at light emission side corresponding to the light emitting diodes having the number same as those of the light-emitting diodes, and light source housings holding a plurality of the light-emitting diodes and a plurality of the collimating optical systems, in which one field lens for covering the collimating optical system is arrange directly after the next collimating optical system (see Patent Document 1).
Patent Document 1: Japanese Patent Application Laid-open No. 2005-203481